The detection of anti-Ro/SS-A and anti-La/SS-B activity of human serum monoclonal immunoglobulins (monoclonal gammopathies).

The sera of 340 patients with monoclonal gammopathies were examined for the presence of anti-Ro/SS-A and anti-La/SS-B activity. An enzyme-linked immunosorbent assay (ELISA) technique was employed. Forty-six sera (13.5%) bound to Ro/SS-A, while 79 sera (23.2%) bound to La/SS-B. The anti-Ro/SS-A and anti-La/SS-B antibodies were found in sera of patients with IgG, IgM, and IgA gammopathies. Forty-two of the 46 sera (91.3%) with positive anti-Ro/SS-A activity were found to bind La/SS-B as well, while only 53.2% (42 out of 79) of the sera that had anti-La/SS-B activity also bound Ro/SS-A. The activity against Ro/SS-A and La/SS-B was further confirmed by immunoblotting with purified immunoglobulins. Antibodies to Ro/SS-A and La/SS-B are common in systemic lupus erythematosus, Sjögren's syndrome, and other rheumatic disorders. Yet none of the patients whose serum was found to contain high titres of anti-Ro/SS-A or anti-La/SS-B human monoclonal antibodies presented with symptoms related to such autoimmune diseases. Our results of a high incidence of anti-Ro/SS-A or anti-La/SS-B activity in the sera of patients with monoclonal gammopathies support previous reports of autoantibody properties characteristic of these immunoglobulins.